RARE EARTH ELEMENT (REE) VARIATION IN FOSSIL AND MODERN BONES: THE INFLUENCE OF OSTEOLOGICAL MATERIALS AND TIME

REE concentrations were measured in various skull materials of an upper Cretaceous mosasaur, Plioplatecarpus (Pierre Shale, Verendrye Member, South Dakota) and an Oligocene oreodont, Merycoidodon (Brule Formation, Badlands National Park, South Dakota) using ICP-MS. Comparisons were made between the REE concentrations of tooth enamel, dentine, traebecular and cortical jaw material. Data for both specimens displayed a consistent pattern of preferential uptake (REE concentrations: cortical > traebecular > dentine > enamel). The REE concentrations in mosasaur cortical bone were as much as fifty times greater than enamel. The REE signatures (REE ratios) in the mosasaur skull materials were identical, varying only within analytical error. Additional analyses were conducted using modern human and deer tooth enamel and dentine, and deer traebecular and cortical jaw material. These specimens display the same consistent preferential uptake as the mosasaur and oreodont. Our findings indicate that although REE concentrations vary according to bone material type, the REE signatures are virtually identical in bones from an individual specimen. These preliminary results suggest that the REE signatures could be used as a tool to relate fossils to their original diagenetic environment. REE concentrations were also measured in modern to progressively older vertebrates, including a modern human, deer, 700 year old fossil bison, and a 12,500 year-old mastodon. Our data indicates REE concentrations increase over time and that REE uptake and apatite recrystallization may be completed within 20-30,000 years. If the REE signature is stable, this suggests that relatively short-term, overlapping taphonomic periods may be discernable within REE signatures. These data underscore the role of bone material type in the relative REE concentrations in an individual specimen, and the influence of time on REE values. The influence of animal type and burial environment on the rate of biogenic apatite recrystallization and REE uptake is also under investigation.